The present invention relates to a technique for automatically switching a current computer to a spare computer in an on-line transaction processing system of a redundantly structured client/server model. More particularly, the invention relates to a switch control method of a redundantly structured system which is suitable for switching the system very reliably when an abnormality occurs.
In a computer system such as a client/server system for executing an on-line transaction process via a network, a redundant structure is usually employed in order to assure the reliability of the system. In the computer system having the redundant structure, another computer system as a spare is prepared for a failure in the current computer system. In the client/server system, when a fault occurs in a current server computer and the connection is switched to a spare server computer, each client computer which receives on-line service has to switch the connection destination address from the address of the current server computer to that of the spare server computer on the basis of a notification from the server computer and then to connect to the spare server computer.
An example of a technique for solving the troublesomeness of the process at the time of switching the system is a technique described in Japanese Patent Application Laid-Open No. 8-235132. In the technique disclosed, a spare host computer controls both of the self address and the address of a current host computer. When a fault occurs in the current host computer, a system switching instruction is transmitted to the spare host computer by a monitoring program. The spare host computer which received the system switching instruction rewrites the self address to the address of the current host computer. In this manner, the system switching operation from the current host computer to the spare host computer is realized. Consequently, the system can be switched from the current host computer to the spare host computer without changing the address of the host computer on the side of a client. According to the technique, however, since the spare host computer rewrites the self address to the address of the current host computer, it is necessary to send a notification of switch control from the current host computer in which a fault occurs to the spare host computer. There is, however, a case such that a monitoring program does not operate normally in the current host computer in which the fault occurs. In this case, the switching operation from the current host computer to the spare host computer cannot be performed.
Generally, the possibility of normal operation of the monitoring program operating in the system in which a fault occurs, especially at the time of a hardware failure, is appreciably diminished.